Up to the present, radar apparatuses have been used for not only locating the present positions of other ships but also observing movements of the other ships by indicating the tracks thereof.
In order to display the track of another ship on the screen of the indicator of a radar apparatus, a prior art method has been used to display on an indicator radar echoes corresponding to tens to a few hundreds of previous radar scans ones over others in a different color from colors for indicating radar echoes obtained with the present or latest radar scan.
FIG. 14 shows an example of an image displayed on the screen of an indicator of a conventional ship track indicating apparatus. As shown in the figure, with conventional ship track indicating apparatii, radar images corresponding to a few tens to a few hundreds of previous radar scans are displayed ones over others so that displayed ship tracks are broadened in width. The width of the ship track becomes wider as the size of a ship becomes larger. This results in a difficulty to distinguish the ship track of each ship from the tracks of the other ships, since the face of the indicator is occupied by many ship tracks. There is another problem that random noises produced with each of a few tens to a few hundreds of radar scans will be accumulated to be displayed on the screen of the indicator, which also makes it difficult to identify the track of another ship.
An object of the present invention is to provide a ship track indicating which is capable of suppressing displayed ship track from being broadened and preventing noise appearances from being accumulated so that each ship track of other ships can be easily identified.
Another object of the present invention is to provide a ship track indicating apparatus which is capable of suppressing ship track images from being widened and easily recognizing from displayed radar echo images characters of radar echoes such as the size of the echoes, the attitude thereof and the like.